Because every feature and parameter would have to be baked into the format and every editor would have to offer those same features and no more.

There's always a trade-off between editability and fidelity with any format. Non-destructive stacks of modifiers bring that trade-off into sharp relief.

Yes.. not only offer the exact same features but any software that tries to implement the format would have to agree on the exact algorithms for the transformations represented by each procedural step. Any error in any one of those algorithms would cascade into subsequent steps and could generate a completely different final product

Some amount of variation is desirable in any artistic endeavor.